Robert Redford's creaky but inevitably absorbing courtroom drama-cum-history lesson gives us a vindictive American government trampling the Constitution in order to avenge a national trauma, then congratulates itself for asking, "Sound familiar?"

Well, yes — tediously familiar. In The Conspirator, Robin Wright stars as Mary Surratt, the Confederate-friendly Maryland woman accused on circumstantial evidence of abetting the plot that killed Abraham Lincoln. As it happens, Surratt ran a boardinghouse frequented by John Wilkes Booth (Toby Kebbell) and his collaborators — including her own son John (Johnny Simmons), who skipped town immediately after the assassination, leaving his mother to get hauled into an unabashedly hostile military tribunal. But at least this Mary Surratt has James McAvoy as Frederick Aiken, a young Union war-hero lawyer who becomes her defender.

In the 146 years since those fateful events at Ford's Theatre first transfixed the American imagination, it's only natural that some of the story's details should have faded from our view. Redford's film does take the trouble to remind us that the conspiracy in question also targeted Vice President Andrew Johnson and Secretary of State William Seward. Otherwise, there's something unsatisfying in how the movie hurries through its pretext, as if too dignified to dwell on the infamous event itself, in order to make its nest in the courtroom and lecture the audience on what to think about what happened thereafter.

Opting always for the obvious over the ambiguous, with rhetoric seemingly lifted from the outraged bumper stickers of the Bush II years, the script lacks the timeless moral force of, say, an Arthur Miller play. It's not like we can really feel Redford yearning for the good old days of big-screen didacticism. It's more like he's on auto-pilot. The one thing a movie with a bleeding heart should not be is bloodless, and this one almost is.

Nobody said it'd be easy to dramatize a battered young nation coming to grips with the value of due process. Or, OK, Redford and Wright may have said that to each other a few times. The evidence displayed suggests they've enjoyed a mutually encouraging if generally unchallenging rapport.

Mostly stashed away among gauzy shafts of light in a sort of 1860s proto-Guantanamo, Wright looks austere and dignified as a martyr to the history we were doomed to repeat. The still-open question of Surratt's possible involvement with the assassination scheme becomes so academic that it's hard not to think she now has suffered the compound injustice of reduction to mere symbolism.

The nice lad playing her lawyer, meanwhile, goes about his conscience-kindling and speechifying with similar constancy. Nudged along by Tom Wilkinson as Reverdy Johnson, the former attorney general who threw the case in his lap, McAvoy's Aiken dutifully altercates with his opponent, the vulpine prosecutor Joseph Holt (Danny Huston), and with the spiteful Secretary of War Edwin Stanton (a cardboard cutout wiggled by Kevin Kline). The equally unchallenged supporting cast also includes Colm Meaney as Gen. David Hunter, who presided over Surratt's trial; Evan Rachel Wood as her long-suffering daughter Anna; and, inexplicably, Justin Long, in a silly mustache, as Aiken's fictive battlefield pal.

Closing credits remind us that the actual Aiken went on, post-Surratt, to rake muck at the Washington Post. Of course, Redford himself did likewise, cinematically, in All The President's Men. So that, too, sounds familiar. Too bad it feels like ancient history.